Conventionally, cooling fans for use in an automobile radiator and the like are often axial fans and diagonal fans. The cooling fans of these types are made of: a bottomed cylindrical boss portion that is rotated by a drive source such as an engine or an electric motor; and a plurality of blades provided on an outer circumferential surface of the boss portion, the blades radiating in a radial direction.
By the way, there is known a cooling fan in which the tips of the blades are connected with each other by means of an annular ring member, to thereby improve the strength of the blades. In such a cooling fan with a ring member provided on the tips of the blades, the blades become heavy. Therefore, the blades are made thinner, to thereby make the blades lighter (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication, First Publication No. 2004-218513
However, in the aforementioned conventional technique, since the blades are made thinner, when the cooling fan is rotated, the thinned blades flap. This poses a problem of worsening the noise characteristic.
In addition, with a ring member provided on the tips of the blades, the cooling fan has a large diameter, which results in the requirement of a dedicated shroud. This poses a problem in which the versatility of the cooling fan is decreased.